With the fast development of industries like petroleum, chemistry, transportation and so on, pipes and cables are widely used. Failures of pipes, such as erosion, perforation or wall thickness reduction, often take place due to high temperature, high pressure, flushing and so on, and reasons like fatigue, raining and so on may cause cables to be broken or corroded. To prevent accidents, it is required to periodically test and maintain the pipes and the cables. Since the ultrasonic guided wave testing technique can fast test a part of the pipe or the cable by a single-point excitation and no need to move sensors during the testing process, it has been widely used in the relevant field.
The magnetostrictive guided wave testing technique has the advantages of no contact, no polishing process on the surface of the tested component, high testing efficiency, and it is applicable for on-site testing of a slender component. U.S. Pat. No. 5,456,113A discloses a method for the nondestructive evaluation of the ferromagnetic material to detect and locate fractures, cracks, and other anomalies based on the magnetostrictive guided waves, U.S. Pat. No. 5,581,037A also discloses a method for the inspection of ferromagnetic cylindrical shell structures such as pipes and pipes based on the magnetostrictive guided waves. The above two testing methods make use of a conventional closed magnetic circuit to axially magnetize the tested cable or pipe, by the way of circumferentially arranging a certain number of magnetizers on the surface to provide a uniform axial static magnetic field. These two methods are non-contact testing methods, namely there is no need to polish the surface of the position for the sensor installation, which results in a high testing efficiency. However, since each magnetizer has large size and heavy weight, it is required to assemble and disassemble multiple magnetizers during the guided wave testing process, which reduces the testing efficiency to a certain extent. Meanwhile, during on-site testing, the number of the tested slender components is always comparatively large, the testing method of using multiple magnetizers to provide the axial static magnetic field has some disadvantages such as inconvenient installation, as well as time-consuming and laborious operation.